What happens in Josephson junctions at high critical current densities

We have studied the current-voltage characteristics of intrinsic Josephson junctions in mesa-shaped Bi 2 Sr 2 CaCu 2 O y and ( Bi 1-x Pb x)2 Sr 2 CaCu 2 O y single crystals as a function of x. Pronounced Josephson tunneling characteristics, which are characterized by high critical current densities and multiple quasiparticle branches with clear subgap structures, have been observed for ( Bi ~0.8 Pb ~0.2)2 Sr 2 CaCu 2 O y. A strong correlation between the characteristics and structural modulation in this system has been found.

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Long Josephson Junctions Modulated by Defects and Superconducting Microdomains in YBCO Thin Films

International Journal of Modern Physics B ◽

10.1142/s0217979299001193 ◽

1999 ◽

Vol 13 (09n10) ◽

pp. 1207-1214

Author(s):

E. Crescio ◽

R. Gerbaldo ◽

G. Ghigo ◽

L. Gozzelino ◽

E. Mezzetti ◽

...

Keyword(s):

Thin Films ◽

High Temperature ◽

Critical Current ◽

Josephson Junctions ◽

Superconducting Films ◽

Coupling Energy ◽

Order Of Magnitude ◽

Current Densities ◽

Hts Films ◽

Random Defect

The critical current Jc of superconducting films is about two order of magnitude larger than that of single crystals. The dependence of such Jc on field depends on the presence and distribution of defects. We speculate that High Temperature Superconducting (HTS) films can be modeled as an agglomeration of islands coupled via Josephson contacts and then considered as a network of Long Josephson Junctions (LJJ) between superconducting islands. In order to check this hypothesis we further developed a model firstly introduced by Fehrenbacher based on the modulation of critical current densities in LJJ by means of suitable distribution of defects. The defects act by modulating the coupling energy of the junction. Critical current densities are calculated in the case of periodic and random defect distributions.

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Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100164155 ◽

1996 ◽

Vol 54 ◽

pp. 338-339

Author(s):

I-Fei Tsu ◽

D.L. Kaiser ◽

S.E. Babcock

Keyword(s):

Grain Boundary ◽

Critical Current Density ◽

Critical Current ◽

Current Density ◽

Electromagnetic Properties ◽

Length Scale ◽

Density Values ◽

Current Densities ◽

Applied Fields ◽

A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

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